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  3. October 2017

RE: Why does USER require VARCHAR and not work with CHAR?

I do not use that keyword. I'll have to look into it though as it seems like a silly default.

I wonder why the RDBMS on iSeries has this parameter when other DB manufacturers don't require it? Is it a case of other RDMBS are smarter about the storage of varchar data and dynamically adjust the allocations in a table based on algorithms?

-----Original Message-----
From: Vernon Hamberg [mailto:vhamberg@xxxxxxxxxxxxxxx]
Sent: Friday, October 13, 2017 10:41 AM
To: midrange-l@xxxxxxxxxxxx
Subject: Re: Why does USER require VARCHAR and not work with CHAR?

Just curious, Matt - do you use the ALLOCATE attribute for VARCHAR columns on the i? It is highly recommended, as Birgitta mentioned in her post here.

I believe this is not part of other RDBMS. And tools generally do not set it when generating tables for use on IBM i. The Default is 0, which results in 2 IOs for each access to the data for each column.

Regards
Vern

On 10/13/2017 9:17 AM, Matt Olson wrote:
I always store everything as varchar so I don't have to constantly be trimming trailing blank spaces in a thousand places in various applications. The CHAR trailing blank space problem leads to bloated software. It forces developers to wrap all their column names in TRIM() command somewhere (either in SQL query or in RPG, .NET, java, etc).

The only case I can think of is CHAR(1). But that might be for putting something like "Y" or "N", which I also loath as that is not automatically translated in higher level languages as a Boolean flag.

Instead of Y/N, its better to use a BIT field (1/0). However DB2 doesn't have BIT database types, so you are left with a less than ideal option of using smallint.

-----Original Message-----
From: Glenn Gundermann [mailto:glenn.gundermann@xxxxxxxxx]
Sent: Thursday, October 12, 2017 4:44 PM
To: Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxx>
Subject: Re: Why does USER require VARCHAR and not work with CHAR?

Hi Matt,

Good comments.
Is it documented as a best practice to use VARCHAR on all character columns?
I.E.
Is there a minimum length for the column to worry about CHAR vs. VARCHAR?
Is there any thinking about the column usage when deciding on CHAR vs.
VARCHAR?


Yours truly,

Glenn Gundermann
Email: glenn.gundermann@xxxxxxxxx
Work: (905) 486-1162 x 239
Cell: (416) 317-3144


On 12 October 2017 at 17:26, Matt Olson <Matt.Olson@xxxxxxxx> wrote:

An additional question is why folks are defining fixed length strings
in any new database files.

I know in most modern programming languages doing string trims on all
those CHAR fields is a major pain in the....

How often have you had to do a TRIM(FirstName) + TRIM(LastName) so
that it shows up as "John Smith" instead of "John
Smith "

It is for that reason I loath CHAR and NCHAR.

I sometimes wonder how many CPU cycles have been burned over time
removing all those blank spaces at the end of CHAR and NCHAR strings.

-----Original Message-----
From: Paul Therrien [mailto:paultherrien@xxxxxxxxxxxxxxxxxx]
Sent: Thursday, October 12, 2017 4:18 PM
To: 'Midrange Systems Technical Discussion' <midrange-l@xxxxxxxxxxxx>
Subject: RE: Why does USER require VARCHAR and not work with CHAR?

Yeah, I realized this after I responded to you. My only thinking on
this is that the 'generate' option somehow forces you to model your
database field after the attributes of the special register.

What if you changed the change_user field to not be a generate-always
field, and allowed it to default like the create_user field?
There would be a chance that someone could overwrite the change_user
field on an insert, but is this something you can live with?




Paul

-----Original Message-----
From: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf
Of Glenn Gundermann
Sent: Thursday, October 12, 2017 4:36 PM
To: Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxx>
Subject: Re: Why does USER require VARCHAR and not work with CHAR?

Hi Paul,

My question is really asking why the first column is okay using CHAR
and the second column not, when both are using the same special register.


Yours truly,

Glenn Gundermann
Email: glenn.gundermann@xxxxxxxxx
Work: (905) 486-1162 x 239
Cell: (416) 317-3144


On 12 October 2017 at 15:08, Paul Therrien <paultherrien@andecosoftware.
com>
wrote:

The USER special register is defined as Varchar(18) so I would guess
anything that uses the User would also need to be varchar(18).

From SQL Reference...
USER
The USER special register specifies the run-time authorization ID at
the current server. The data type of the special register is
VARCHAR(18).


Paul

-----Original Message-----
From: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf
Of Glenn Gundermann
Sent: Thursday, October 12, 2017 2:48 PM
To: Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxx>
Subject: Why does USER require VARCHAR and not work with CHAR?

Hi there,

IBM i 7.3, TR 2, cum level 17061, DB2 PTF group level 6

I have a CREATE TABLE statement where the create user column is
using
CHAR(18) and the change user column won't allow CHAR(18) but works
if VARCHAR(18).
Why can't they both be CHAR(18)?

This won't work:

CREATE OR REPLACE TABLE glenn_test_table FOR SYSTEM NAME test_table (
create_user FOR COLUMN recrtuser CHAR(18) CCSID 37 NOT NULL
DEFAULT USER ,
change_user FOR COLUMN rechguser CHAR(18) CCSID 37 NOT NULL
GENERATED ALWAYS AS (USER) )
RCDFMT RPCMMNT

SQL0574 Column, sequence, or variable attribute is not valid.

This does work:

CREATE OR REPLACE TABLE glenn_test_table FOR SYSTEM NAME test_table (
create_user FOR COLUMN recrtuser CHAR(18) CCSID 37 NOT NULL
DEFAULT USER ,
change_user FOR COLUMN rechguser VARCHAR(18) CCSID 37 NOT NULL
GENERATED ALWAYS AS (USER) )
RCDFMT RPCMMNT

My question, why?


Yours truly,

Glenn Gundermann
Email: glenn.gundermann@xxxxxxxxx
Work: (905) 486-1162 x 239
Cell: (416) 317-3144
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